Castable high explosives are usually prepared by combining an explosive ingredient, such as a nitramine, with a curable binder and optionally a reactive metal and an oxidizer. One widely used binder is hydroxy terminated polybutadiene (HTPB). HTPB is cured using conventional diisocyanate curing agents and cure catalysts. A typical HTPB explosive is PBXN-109, which contains 20 wt. % Aluminum, 64 wt. % RDX (1,3,5-trinitro-1,3,5-triazacyclohexane), and 16 wt. % binder system containing HTPB, DOA (dioctyladipate), and IPDI (isophorone diisocyanate). As shown in this example, the binder system may also contain a plasticizer to aid processing. Once the ingredients are mixed, the cure reaction begins which causes viscosity to increase until the polymer is fully cured. PBXN-109 has a detonation velocity of about 7600 m/s.
The pot life, i.e., the handling time available between mixing and when the composition begins to set up, and cure time of the binder system is dependent on the specific materials used, the mixing and curing temperature, the size of the cured product, and the catalyst concentration. Pot life is typically defined as the point at which the viscosity reaches 40 kP as measured by a Brookfield viscometer. A minimum pot life of 6-10 hours is typically desired to allow casting of the explosive into military warheads. Curing time is dependent upon many factors, but is typically carried out within a week at a typical curing temperature from 135.degree. F. to 145.degree. F. Short cure times are desired for reasons of economy.
There are disadvantages associated with typical cast explosives described above. For instance, because HTPB is an inert binder, it does not enhance the energetic performance of the high explosive composition. In addition, the need for a curing agent and/or cure catalyst not only diminishes the energetic performance, but also complicates the mixing and processing. Moreover, isocyanate curing agents are susceptible to moisture contamination, and cure catalysts are easily poisoned.
Other cast explosives are prepared from nitrocellulose ("NC") binder systems, such as those described in U.S. Pat. No. 3,943,017 to Wells. The Wells binder systems include a small amount of nitrocellulose and a large amount of liquid plasticizer. The ratio of plasticizer to nitrocellulose is from 6.5:1 to 15:1. The reason Wells requires such large amounts of plasticizer is because nitrocellulose begins to swell and gelate immediately during mixing. Plasticizers are needed to keep the viscosity low enough to permit processing.
A Navy explosive, PBXN-103, is prepared with a plastisol grade nitrocellulose ("PNC") binder. PBXN-103 has the following ingredients:
______________________________________ Ingredient Weight Percent ______________________________________ Ammonium perchlorate 40 Aluminum 27 TMETN 23 TEGDN 2.5 PNC 6 Ethyl centralite 1.3 Resorcinol 0.2 ______________________________________
TMETN (trimethylolethanetrinitrate) and TEGDN (triethyleneglycoldinitrate) are energetic plasticizers. Ethyl centralite and resorcinol are stabilizers. PBXN-103 hardens via gelation or physical bonding rather than by chemical cross-linking. PBXN-103 is designed for underwater use or other low oxygen environments. It contains a large amount of ammonium perchlorate and aluminum to provide the high combustion temperature. The PBXN-103 explosive also contains high quantities of plasticizer relative to the PNC binder. PBXN-103 is a low brisance explosive, having a relatively low detonation velocity of about 6000 m/s. Because of the low detonation velocity, PBXN-103 is not well suited for use in high performance precision shaped charges and EFP's (explosively formed penetrators).
From the foregoing, it would be an advancement in the art to provide a high performance castable explosive which is easily processed and which produces a high detonation velocity suitable for use in shaped charge, explosively formed penetrator warhead, fragmentation warhead, and mine clearing charge applications.
Such high performance castable high explosive compositions are disclosed and claimed herein.